Coated filaments and their manufacture

Abstract

A coating is formed by chemical vapour deposition an electrically heated filament which is passed through an end plate into a deposition chamber and leaves the deposition chamber through a similar end plate. The filament slides through an entrance passage into a first electrode chamber, around part of a wheel electrode into the deposition chamber. The passage of the filament around the wheel electrode provides adequate direct electrical contact. The end plate operates in exactly the same manner. As no mercury or a low-melting point eutectic alloy is used, no contaminants associated therewith are produced and the resultant coated filament is free of such contaminants.

1 . Filament coating apparatus comprising:
 a deposition chamber in which a coating is to be applied to a filament;   a first electrode chamber having:
 an entrance passage permitting said filament to slide into said first electrode chamber; 
 an exit passage permitting said filament to slide from said first electrode chamber into said deposition chamber; 
   a second electrode chamber having:
 an entrance passage permitting said coated filament to slide out of said deposition chamber into said second electrode chamber; 
 an exit passage permitting said coated filament to slide out of said second electrode chamber; 
   said first electrode chamber housing a first roller electrode means providing direct electrical contact with said filament; and   said second electrode chamber housing a second roller electrode means providing direct electrical contact with said coated filament.   
     
     
         2 . Filament coating apparatus, as in  claim 1 , having sealing means to inhibit the escape of gas from said deposition chamber into either of said electrode chambers. 
     
     
         3 . Filament coating apparatus, as in  claim 2 , having a gas inlet to supply gas to each of said electrode chambers at a pressure greater than an operational pressure within said deposition chamber. 
     
     
         4 . Filament coating apparatus, as in  claim 2 , in which each of said electrode chambers has a gas outlet to reduce gas pressure within said electrode chambers to below ambient atmospheric pressure. 
     
     
         5 . Filament coating apparatus, as in  claim 2 , in which each of said sealing means comprises a gas outlet for any gas escaping from said deposition chamber into said electrode chamber. 
     
     
         6 . Filament coating apparatus comprising:
 a deposition chamber in which a coating is to be applied to a filament;   a first electrode chamber having:
 an entrance passage permitting said filament to slide into said first electrode chamber; and 
 an exit passage permitting said filament to slide from said first electrode chamber into said deposition chamber; 
   a second electrode chamber having:
 an entrance passage permitting said coated filament to slide out of said deposition chamber into said second electrode chamber; and 
 an exit passage permitting said coated filament to slide out of said second electrode chamber; 
   said first electrode chamber housing a first electrode wheel positioned relative to its said entrance passage and its said exit passage to ensure direct electrical contact said filament; and   said second electrode chamber housing a second electrode wheel positioned relative to its said entrance passage and its said exit passage to ensure direct electrical contact with said coated filament.   
     
     
         7 . Filament coating apparatus, as in  claim 6 , in which said entrance passage to the first electrode chamber and said exit passage from the second electrode chamber are both horizontal. 
     
     
         8 . Filament coating apparatus comprising:
 a deposition chamber in which a coating is to be applied to a filament;   a first electrode chamber having:
 an entrance passage permitting said filament to slide into said first electrode chamber; and 
 an exit passage permitting said filament to slide from said electrode chamber into said deposition chamber; 
   a second electrode chamber having:
 an entrance passage permitting said coated filament to slide out of said deposition chamber into said second electrode chamber; and 
 an exit passage permitting said coated filament to slide out of said second electrode chamber; 
   said first electrode chamber housing at least two electrode wheels positioned to engage opposite sides of the filament to ensure direct electrical contact with the filament; and   said second electrode chamber housing at least two further electrode wheels positioned to engage opposite sides of the coated filament to ensure direct electrical contact with the coated filament.   
     
     
         9 . Filament coating apparatus, as in  claim 8 , in which said first electrode chamber houses three of said electrode wheels positioned such that two of said electrode wheels are pressed against one side of said filament and the third of said electrode wheels is pressed against the opposite side of said filament in a position between the said two electrode wheels. 
     
     
         10 . Filament coating apparatus, as in  claim 8 , in which said second electrode chamber houses three of said electrode wheels positioned such that two of said electrode wheels are pressed against one side of said coated filament and the third of said electrode wheels is pressed against the opposite side of said coated filament in a position between the said two electrode wheels. 
     
     
         11 . Filament coating apparatus, as in  claim 8 , in which at least some of said electrode wheels are positioned to guide said filament into alignment with said exit passage from said first electrode chamber and to guide said coated filament into alignment with said exit passage from said second electrode chamber. 
     
     
         12 . Filament coating apparatus comprising:
 a deposition chamber in which a coating is to be applied to a filament;   a first electrode chamber having:
 an entrance passage permitting said filament to slide into said first electrode chamber; and 
 an exit passage permitting said filament to slide from said first electrode chamber into said deposition chamber; 
   a second electrode chamber having:
 an entrance passage permitting said coated filament to slide out of said deposition chamber into said second electrode chamber; and 
 an exit passage permitting said coated filament to slide out of said second electrode chamber; and 
   said first electrode chamber housing a roller electrode mounted for rotation about an axis oblique to a line between the entrance passage to said first electrode chamber and the exit passage from said first electrode chamber whereby said filament can be wound around said roller electrode to ensure adequate direct electrical contact.   
     
     
         13 . Filament coating apparatus, as in  claim 12 , in which the roller electrode has a spiral surface for engaging the filament. 
     
     
         14 . Filament coating apparatus, as in  claim 12 , in which said second electrode chamber houses a second roller electrode mounted for rotation about an axis oblique to a line between the entrance passage to said second electrode chamber and the exit passage from said second electrode chamber whereby said coated filament can be wound around said second roller electrode to ensure adequate direct electrical contact. 
     
     
         15 . Filament coating apparatus, as in  claim 14 , in which said second roller electrode has a spiral surface for engaging the coated filament. 
     
     
         16 . A method of coating a filament including:
 passing an electrically-conductive filament over a first roller electrode into a deposition chamber;   withdrawing the coated filament from said deposition chamber over a second roller electrode;   using said first roller electrode to establish direct electrical contact with said filament;   using said second roller electrode to establish direct electrical contact with said coated filament to provide an electrical heating circuit through the filament; and   passing at least one thermally-reactive gas into said deposition chamber to form the coating by chemical vapour deposition.   
     
     
         17 . A method of coating a filament including:
 passing an electrically-conductive filament over a first roller electrode;   withdrawing the coated filament from said deposition chamber over a second roller electrode; and   using the first roller electrode to establish an electrostatic circuit to cause physical vapour deposition of the coating from material within the said deposition chamber.